Method for impregnating decorative papers

ABSTRACT

A method for impregnating decorative papers which are used for producing highly abrasion-proof laminate floor materials. The decorative paper is first moistened with an amino resin and is thus impregnated. The amount of resin applied is controlled using dosing rollers. In addition, a layer including an amino resin is sprayed with a special dispersion onto the moistened decorative paper. The final mass per unit area with regard to the dry mass of the base paper ranges from 100% to 250%.

BACKGROUND

The invention relates to a method of impregnating decorative orpatterned papers used for the production of highly wear-resistantlaminate flooring materials, in which the decorative paper is firstmoistened and impregnated with an amino resin as well as the resincontent being regulated in this step.

It is known (patent of Graudenz et al.), to produce highlywear-resistant decorative paper impregnates for laminate flooringmaterials. In this known process, after the actual impregnation, thereis applied to the patterned paper a mass in which the particulatecorundum is held relatively stable by special viscosity-increasingsubstances in a dispersion forming the mass.

In this arrangement the mass is applied by means of spreading rollersstill in the wet phase directly after the impregnation or alternativelyin an intermediate drying stage.

In this known technology making use of spreading rollers thecorundum-containing mass is present in reservoir vessels in which thereare formed dead zones, in which there is little movement of the mass.Accordingly the corundum particles settle out, which has the consequenceof a lack of homogeneity in the application of the corundum to the paperand thereby substantial variations in the wear resistance values of theresulting laminate flooring materials.

For this reason hitherto viscosity-increasing substances, as a rulecellulose derivatives, have been added to the mass containing thecorundum mixture. Furthermore the corundum should be relatively fine, asthe lighter or finer corundum particles are less rapidly precipitated.However the introduction of cellulose derivatives leads to an opticaldulling of the surface of the laminate flooring materials produced.

The finer the particle size of the corundum, the more must be theproportion of it applied to the decorative paper in order to achievesufficient wear resistance. Also this results in a dulling of thesurface of the materials produced.

SUMMARY OF THE INVENTION

The invention is based on solving the problem of avoiding theabove-mentioned drawbacks of the known manufacture of highlywear-resistant laminate flooring materials and to be able to producehighly wear-resistant decorative laminate flooring materials, thedecorative paper which exhibits the surface structure being at the sametime coated with particulate corundum without the surface of theflooring materials thus produced showing any dulling.

The above-mentioned problem is solved by a method of impregnating paperused for the production of wear-resistant laminate flooring materialcomprising the steps of: a) taking paper; b) damping and impregnatingsaid paper with an amino resin by the use of metering rollers; and c)additionally spraying onto said damped wet paper an additional layer ofamino resin in a dispersion containing an abrasive substance and aflow-promoting agent; and wherein the final area density relative to thedry mass of raw paper amounts to 100% to 250%. As is preferred, thedispersion comprises 100 parts of the amino resin, 20 to 95 parts of theabrasive substance, 0.5 to 2.5 parts of a silane adhesion promoter, 5 to25 parts of a flow-promoting agent, 0.1 to 0.4 parts of a wetting agent,0.05 to 0.4 parts of a separating agent and of an amino resin hardener.

Further in accordance with the invention, a melamine resin is employedas the amino resin, and polyglycol ether, e-caprolactam or butane diolis employed as the flow-promoting agent, and the abrasive substancecomprises at least one of aluminium oxide and silicon carbide having amean particle size of 60 to 160 μ-m. In addition, a mixture of siliconcarbide and aluminium oxide can be employed as the abrasive substance,and after the spraying step the impregnated paper can be pressed to forma panel.

One of the important differences of the process according to theinvention lies in the fact that the mass or dispersion used forimpregnating the decorative paper and for applying the wear-resistantbodies such as corundum particles is sprayed on or applied by the nozzleprinciple.

The nozzle principle has the advantage over application by rolling thatthe dispersion containing the wear-resistant bodies such as corundumparticles is continuously and thoroughly stirred around beforeapplication and thereby is more or less uniformly moved. Accordinglyappearances of deposits which lead) to a lack of uniformity are notobserved. Therefore also one can dispense with the addition ofviscosity-increasing materials or substances. On the contrary in factone can introduce flow-promoting materials which achieve an improveddistribution of the wear-resistant material such as corundum, which isof advantage in the press used for compressing the material.

A further advantage lies in the fact that one does not need to payparticular attention to using aluminium oxide of a particularly fineparticle size, but that corundum or other particulate wear-resistantmaterial having a significantly larger or coarser particle size can beemployed. This has the further consequence that relatively smallquantities of corundum or other particulate wear-resistant material arerequired in order to achieve high values of wear-resistance.

The consequence of these measures and advantages is that particularlytransparent and brilliant surfaces of laminate flooring materials can beachieved according to the invention.

A further advantage of the invention lies in the fact that one does not,as in the known application of the mass or dispersion used forimpregnation by means of spreading rollers, have to proceed with arelatively slow impregnation velocity of for example 18 to 25 m/min, inorder to achieve an adequately uniform application, but that using theprocess according to the invention, in which the mass or dispersion issupplied by means of nozzles, one can achieve or realise impregnationvelocities of 40 to 50 m/min.

DETAILED DESCRIPTION

The invention is further explained in the following in conjunction withembodiments by way of example.

EXAMPLE 1

A special dispersion is first pre-mixed in a reservoir vessel havingstirring means. Stirred into this are 200 kg melamine resin (Kauraminsoaking resin 786 from Messrs BASF), 10 kg water, 1.5 kg of a wettingagent, 0.4 kg of a separating agent and 1.5 kg hardener (H 527 fromMessrs BASF). Then there is added 80 kg, corundum having a mean particlesize of 135 μ-m. After 10 minutes of stirring 25 kg of ε-caprolactam and0.9 kg of a commercially available silane adhesion promoter are added.

A standard impregnating channel made by Messrs VITS is providedfollowing the impregnating means with feed-in means comprising a wideroller, a direction-reversing roller, a nozzle gap with receivingvessel, a pair of metering rollers as well as wire supporting rollers.

A decorative or patterned paper web having a density of 70 g/m² is fedthrough the impregnating equipment and the additional structure. In thestandard impregnating equipment an initial resin take-up of 75 g/m²(obtained after drying) is set. When this value is reached the nozzle isset in operation and the special dispersion is applied. Through thesecond pair of metering rollers a final mass of 155 g/m² is set. Thepaper treated in this way is conducted through a drier at a speed of 45m/min. The residual moisture content amounts to 6.1%.

The decorative or patterned paper is subsequently pressed in a shortstroke press to form an HDF supporting plate (pressing temperature 180°C., pressing time 20 s). There is obtained a brilliant surface whichfulfils the requirements of pr-EN 13329 and has a wear-resistance valueof IP 12,000.

Example 2

Like Example 1. Instead of corundum, particulate silicon carbide havinga mean particle size of 125 μ-m is used. A dark-coloured decorativepaper is employed.

Example 3

Like Example 1. However instead of corundum there is used a mixture of75% aluminium oxide having a mean particle size of 125 μ-m and 25%silicon carbide having the same mean particle size.

I claim:
 1. A method of impregnating paper used for the production of wear-resistant laminate flooring material comprising: a) taking paper; b) damping and impregnating said paper with an amino resin by the use of metering rollers; and c) additionally spraying onto said damped wet paper an additional layer of amino resin in a dispersion containing an abrasive substance and a flow-promoting agent; and wherein the final area density relative to the dry mass of raw paper amounts to 100% to 250%; and wherein the dispersion comprises 100 parts of the amino resin, 20 to 95 parts of the abrasive substance, 0.5 to 2.5 parts of a silane adhesion promoter, 5 to 25 parts of a flow-promoting agent, 0.1 to 0.4 parts of a wetting agent, 0.05 to 0.4 parts of a separating agent and of an amino resin hardener.
 2. A method according to claim 1, wherein a melamine resin is employed as the amino resin.
 3. A method according to claim 1, wherein polyglycol ether, e-caprolactam or butane diol is employed as the flow-promoting agent.
 4. A method of impregnating paper used for the production of wear-resistant laminate flooring material comprising: a) taking paper; b) damping and impregnating said paper with an amino resin by the use of metering rollers; and c) additionally spraying onto said damped wet paper an additional layer of amino resin in a dispersion containing an abrasive substance; wherein the final area density relative to the dry mass of raw paper amounts to 100% to 250%; wherein the abrasive substance comprises at least one of aluminium oxide and silicon carbide having a mean particle size of 60 to 160 μ-m; and wherein the dispersion comprises 100 parts of the amino resin, 20 to 95 parts of the abrasive substance, 0.5 to 2.5 parts of a silane adhesion promoter, 5 to 25 parts of a flow-promoting agent, 0.1 to 0.4 parts of a wetting agent, 0.05 to 0.4 parts of a separating agent and of an amino resin hardener.
 5. A method according to claim 1, wherein a mixture of silicon carbide and aluminium oxide is employed as the abrasive substance.
 6. A method according to claim 1, wherein, after the spraying step, the impregnated paper is pressed to form a panel. 